Re: [Qemu-devel] [PATCH v9 3/6] target/ppc: Handle NMI guest exit

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, May 29, 2019 at 11:10:32AM +0530, Aravinda Prasad wrote:
> Memory error such as bit flips that cannot be corrected
> by hardware are passed on to the kernel for handling.
> If the memory address in error belongs to guest then
> the guest kernel is responsible for taking suitable action.
> Patch [1] enhances KVM to exit guest with exit reason
> set to KVM_EXIT_NMI in such cases. This patch handles
> KVM_EXIT_NMI exit.
> 
> [1] https://www.spinics.net/lists/kvm-ppc/msg12637.html
>     (e20bbd3d and related commits)
> 
> Signed-off-by: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
> ---
>  hw/ppc/spapr.c          |    1 +
>  hw/ppc/spapr_events.c   |   23 +++++++++++++++++++++++
>  hw/ppc/spapr_rtas.c     |    5 +++++
>  include/hw/ppc/spapr.h  |    6 ++++++
>  target/ppc/kvm.c        |   16 ++++++++++++++++
>  target/ppc/kvm_ppc.h    |    2 ++
>  target/ppc/trace-events |    1 +
>  7 files changed, 54 insertions(+)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index fae28a9..6b6c962 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1809,6 +1809,7 @@ static void spapr_machine_reset(void)
>  
>      spapr->cas_reboot = false;
>  
> +    spapr->mc_status = -1;
>      spapr->guest_machine_check_addr = -1;
>  
>      /* Signal all vCPUs waiting on this condition */
> diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c
> index ae0f093..a18446b 100644
> --- a/hw/ppc/spapr_events.c
> +++ b/hw/ppc/spapr_events.c
> @@ -620,6 +620,29 @@ void spapr_hotplug_req_remove_by_count_indexed(SpaprDrcType drc_type,
>                              RTAS_LOG_V6_HP_ACTION_REMOVE, drc_type, &drc_id);
>  }
>  
> +void spapr_mce_req_event(PowerPCCPU *cpu, bool recovered)
> +{
> +    SpaprMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());

You ignore the 'recovered' parameter, is that right?

> +    while (spapr->mc_status != -1) {
> +        /*
> +         * Check whether the same CPU got machine check error
> +         * while still handling the mc error (i.e., before
> +         * that CPU called "ibm,nmi-interlock")
> +         */
> +        if (spapr->mc_status == cpu->vcpu_id) {
> +            qemu_system_guest_panicked(NULL);
> +            return;
> +        }
> +        qemu_cond_wait_iothread(&spapr->mc_delivery_cond);
> +        /* Meanwhile if the system is reset, then just return */
> +        if (spapr->guest_machine_check_addr == -1) {
> +            return;
> +        }
> +    }
> +    spapr->mc_status = cpu->vcpu_id;
> +}
> +
>  static void check_exception(PowerPCCPU *cpu, SpaprMachineState *spapr,
>                              uint32_t token, uint32_t nargs,
>                              target_ulong args,
> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
> index e7509cf..e0bdfc8 100644
> --- a/hw/ppc/spapr_rtas.c
> +++ b/hw/ppc/spapr_rtas.c
> @@ -379,6 +379,11 @@ static void rtas_ibm_nmi_interlock(PowerPCCPU *cpu,
>          /* NMI register not called */
>          rtas_st(rets, 0, RTAS_OUT_PARAM_ERROR);
>      } else {
> +        /*
> +         * vCPU issuing "ibm,nmi-interlock" is done with NMI handling,
> +         * hence unset mc_status.
> +         */
> +        spapr->mc_status = -1;
>          qemu_cond_signal(&spapr->mc_delivery_cond);
>          rtas_st(rets, 0, RTAS_OUT_SUCCESS);
>      }
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index 9dc5e30..fc3a776 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -190,6 +190,11 @@ struct SpaprMachineState {
>  
>      /* State related to "ibm,nmi-register" and "ibm,nmi-interlock" calls */
>      target_ulong guest_machine_check_addr;
> +    /*
> +     * mc_status is set to -1 if mc is not in progress, else is set to the CPU
> +     * handling the mc.
> +     */
> +    int mc_status;
>      QemuCond mc_delivery_cond;
>  
>      /*< public >*/
> @@ -793,6 +798,7 @@ void spapr_clear_pending_events(SpaprMachineState *spapr);
>  int spapr_max_server_number(SpaprMachineState *spapr);
>  void spapr_store_hpte(PowerPCCPU *cpu, hwaddr ptex,
>                        uint64_t pte0, uint64_t pte1);
> +void spapr_mce_req_event(PowerPCCPU *cpu, bool recovered);
>  
>  /* DRC callbacks. */
>  void spapr_core_release(DeviceState *dev);
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 3bf0a46..39f1a73 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -1761,6 +1761,11 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
>          ret = 0;
>          break;
>  
> +    case KVM_EXIT_NMI:
> +        trace_kvm_handle_nmi_exception();
> +        ret = kvm_handle_nmi(cpu, run);
> +        break;
> +
>      default:
>          fprintf(stderr, "KVM: unknown exit reason %d\n", run->exit_reason);
>          ret = -1;
> @@ -2844,6 +2849,17 @@ int kvm_arch_msi_data_to_gsi(uint32_t data)
>      return data & 0xffff;
>  }
>  
> +int kvm_handle_nmi(PowerPCCPU *cpu, struct kvm_run *run)
> +{
> +    bool recovered = run->flags & KVM_RUN_PPC_NMI_DISP_FULLY_RECOV;
> +
> +    cpu_synchronize_state(CPU(cpu));
> +
> +    spapr_mce_req_event(cpu, recovered);

Urgh.. KVM calling directly into spapr code isn't conceptually
correct, although it's usually kind of ok in practice.  I guess we
already do it for hypercalls, so this is no worse.  If we ever have
NMI events for KVM PR or BookE KVM which could happen for non-PAPR
guests, I guess we'll need to re-examine this.

> +    return 0;
> +}
> +
>  int kvmppc_enable_hwrng(void)
>  {
>      if (!kvm_enabled() || !kvm_check_extension(kvm_state, KVM_CAP_PPC_HWRNG)) {
> diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
> index 45776ca..18693f1 100644
> --- a/target/ppc/kvm_ppc.h
> +++ b/target/ppc/kvm_ppc.h
> @@ -81,6 +81,8 @@ bool kvmppc_hpt_needs_host_contiguous_pages(void);
>  void kvm_check_mmu(PowerPCCPU *cpu, Error **errp);
>  void kvmppc_set_reg_ppc_online(PowerPCCPU *cpu, unsigned int online);
>  
> +int kvm_handle_nmi(PowerPCCPU *cpu, struct kvm_run *run);
> +
>  #else
>  
>  static inline uint32_t kvmppc_get_tbfreq(void)
> diff --git a/target/ppc/trace-events b/target/ppc/trace-events
> index 3dc6740..6d15aa9 100644
> --- a/target/ppc/trace-events
> +++ b/target/ppc/trace-events
> @@ -28,3 +28,4 @@ kvm_handle_papr_hcall(void) "handle PAPR hypercall"
>  kvm_handle_epr(void) "handle epr"
>  kvm_handle_watchdog_expiry(void) "handle watchdog expiry"
>  kvm_handle_debug_exception(void) "handle debug exception"
> +kvm_handle_nmi_exception(void) "handle NMI exception"
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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